怎样将jpg文件转换为bmp文件？

JpegImage:TJPEGImage;
BitmapImage:TBitmap;
JpegImage:=TJPGEImage.Create();
Bitmap:=TBitmap.Create();
JpegImage.LoadFromFile('D:\test.jpeg');
Bitmap.Assign(JpegImage);
Bitmap.SaveToFile('D:\test.bmp');
JpegImage.Free;
JpegImage:=nil;
BitmapImage.Free;
BitmapImage:=nil;